Understanding LIDAR Technology Brian Mayfield, CP, GISP, GLS Timothy A. Blak, GS, PLS, CFM

Brief Introductions Brian Mayfield, CP, GISP, GLS Dewberry Program Manager to VGIN Tim Blak, GS, PLS, CFM Appendix A of the Map Modernization Guidelines (http://www.fema.gov/pdf/fhm/frm_gsaa.pdf) NDEP (National Digital Elevation Program) Guidelines for Digital Elevations Data (http://www.ndep.gov/NDEP_Elevation_Guidelines_Ver1_10May2004.pdf)

Our Role in the Industry Trusted Advisor North Carolina Maryland Mapping Solutions Provider USGS GPSC NOAA CSC FEMA Regional IDIQ Study Contractor Not a Mapping Firm No Acquisition Resources (not tied to any specific technologies or brands) Industry Leading QA/QC Services NOAA Statewides

What is LIDAR LIght Detection And Ranging Active Sensing System Uses its own energy source Measures range distances Based on time between emission, reflection and receive time Direct terrain measurements, unlike photogrammetry which is inferred Day or night operation except when coupled with digital camera LiDAR provides a point cloud with X.Y,Z positions

What LIDAR is NOT All-weather Able to “penetrate vegetation” Target must be visible within the selected EM spectrum No rain or fog Must be below clouds Able to “penetrate vegetation” LIDAR can penetrate openings in the vegetation cover but cannot see through closed canopies

Animation

LIDAR Components Three major components of a LIDAR system GPS Inertial Measurement Unit Laser Range Finder

Laser Returns First Last Intermediate Ideal for surface models Ideal for generating bare-earth terrain models Intermediate Ideal for determining vegetation structure

Laser Returns Courtesy of EarthData Technologies

LIDAR data points - X, Y, Z Top View Side View Courtesy of Terrapoint

Intensity Images Measures the amount of light returning to the sensor Developing technology – infancy stage Can now be used for stereo-compilation to generate 3D breaklines (“LIDARgrammetry)

Intensity Imagery

Full Point Cloud Surface Model

Surface Model

Cityscape Surface Model

Cityscape Ground Model

Full Point Cloud Surface Model

LIDAR Uses Courtesy of Terrapoint

LIDAR Uses

Accuracy Standards FEMA – Guidelines and Specification for Flood Hazard Mapping Partners Appendix A: Guidance for Aerial Mapping and Surveying NDEP Guidelines For Digital Elevation Data

FEMA’s Criteria for Topographic Data For either photogrammetry or LIDAR: Accuracy equivalent to 2’ contours or better for flat terrain (Accuracyz = 1.2’ at 95% confidence level) Vertical accuracy at 95% confidence level = Accuracyz = 1.9600 x RMSEz Accuracy equivalent to 4’ contours or better for rolling to hilly terrain (Accuracyz = 2.4’ at 95% conf level)

Accuracy Equivalencies NMAS Contour Interval 90% Conf NSSDA 95% RMSEz 2’ 1’ 1.2’ 0.6’ 18.5 cm 4’ 2.4’ 37.0 cm

Quantitative Verification NDEP Standards as of Jan. 2003 Fundamental Vertical Accuracy. For open terrain only, compute RMSEz. Report Accuracyz as: “Tested __ (meters, feet) Fundamental Vertical Accuracy at 95% confidence level in open terrain based on RMSEz x 1.9600.” Supplemental Vertical Accuracy. For all other land cover categories, determine 95th percentile error(s). Report Accuracyz as: “Tested __ (meters, feet) Supplemental Vertical Accuracy at 95th percentile in weeds, crops, scrub, forests, urban areas, etc.” and document outliers. AND/OR Consolidated Vertical Accuracy. Report Accuracyz as: “Tested __ (meters, feet) Consolidated Vertical Accuracy at 95th percentile in open terrain, weeds, crops, scrub, forests, urban areas, etc.” and document outliers.

Contours Once the elevation model is created - contours are just a click away…or are they? The key to creating good contours is to control their behavior Controlling their behavior can be expensive using traditional methods New methodologies are being developed for LIDAR such as hydro-enforced contours or by “LIDARgrammetry”

Contours Two Types of Contours Engineering Topographic

LIDAR Contours

Breaklines Linear features that control surface behavior Can be 2D or 3D Traditionally derived from stereo photogrammetry or from surveys Can use LIDAR and Intensity to create breaklines or can use Hydro-enforced method

Pricing

Questions?